I'm not affiliated with this project at all, but some chap has recently developed a podcast app that's worth checking out. It's free and without restrictions and is able to sync those pesky podcasts that aren't available through spotify (BBC podcasts, France-Inter podcasts etc)
Link to download:
https://apps.garmin.com/en-US/apps/b5b85600-0625-43b6-89e9-1245bd44532c
Link to the open source project:
https://github.com/lucasasselli/garmin-podcasts
Seems to work well at the moment even though it hasn't even been in development for very long.